Surface defect inspection method and apparatus

ABSTRACT

A surface defect inspection apparatus and method for irradiating a beam multiple times to a same region on a surface of an inspection sample, detecting each scattered light from the same region by detection optical systems individually to produce plural signals, and wherein irradiating the beam includes performing a line illumination of the beam on a line illumination region of the sample surface. The line illumination region is moved in a longitudinal direction at a pitch shorter than a length of the line illumination region in the longitudinal direction.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/221,314, filed Aug. 30, 2011, which, in turn, is a continuation ofU.S. application Ser. No. 12/727,752, filed Mar. 19, 2010 (now U.S. Pat.No. 8,035,808), which, in turn, is a continuation of U.S. applicationSer. No. 12/109,548, filed Apr. 25, 2008 (now U.S. Pat. No. 7,710,557),and which application claims priority from Japanese Application JP2007-115004 filed on Apr. 25, 2007 and Japanese Application JP2007-156385 filed on Jun. 13, 2007, the contents of which are herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a surface defect inspection method anda surface defect inspection apparatus for detecting a tiny foreignmatter/defect on the surface of the semiconductor substrate and the likewith high sensitivity at high speeds.

On the manufacturing line of the semiconductor substrate or the thinfilm substrate, the inspection with respect to the defect and foreignmatter on the surface of the semiconductor substrate or the thin filmsubstrate is performed for the purpose of maintaining and furtherimproving the product yield. For example, the sample of thesemiconductor substrate prior to formation of the circuit patternrequires detection of the tiny defect or foreign matter with the sizeequal to or smaller than 0.05 μm on the surface. It is essential toperiodically inspect whether or not the tiny defect or the foreignmatter exists in the respective step of the manufacturing facility inorder to improve the production yield.

The generally employed inspection apparatus as disclosed in JP-A9-304289 and 2000-162141, and U.S. Pat. No. 5,903,342 is structured toirradiate the laser beam of several tens μm focused on the surface ofthe sample so as to condense and detect the scattered light from thedefect or the foreign matter. With the art for classifying the defecttype has been disclosed in Japanese Unexamined Patent ApplicationPublication No. 2001-255278 or U.S. Pat. No. 6,894,302, the scatteredlight from the defect is multi-directionally detected so as to identifythe directionality of the scattered light.

SUMMARY OF THE INVENTION

A problem to be solved by the present invention will be described. Thedistribution of the scattered light caused by the defect with the sizecorresponding to 1/10 of the illumination wavelength becomes isotropic.So the SN ratio is improved by adding the multi-directionally detectedsignals, which makes it possible to detect the tiny defect. Meanwhile,the defect which causes the distribution of the scattered light to beanisotropic reduces the SN ratio by adding the multi-directionallydetected signals, thus lowering the detection sensitivity. The surfacedefect inspection with respect to the semiconductor substrate isrequired to be performed with high sensitivity irrespective of thedefect type.

The tiny defect inspection is performed by adding the detection signalsof the multi-directionally detected scattered lights, and the respectivedetected signals are individually processed so as to avoid the errorfailing to detect the anisotropic defect. The specific structures willbe described hereinafter.

According to the first aspect of the structure, in a surface defectinspection apparatus, a laser beam focused on a surface of an inspectionsample is irradiated, a scattered light generated on the surface of theinspection sample is multi-directionally condensed, and the condensedscattered light is photoelectrically converted to inspect a defect whichexists on the surface of the inspection sample. Multi-directionallydetected detection signals are added to detect a tiny defect. Each ofthe multi-directionally detected detection signals is individuallyprocessed to detect an anisotropic defect.

According to the second aspect of the structure, in a surface defectinspection apparatus, a laser beam focused on a surface of an inspectionsample is irradiated, a scattered light generated on the surface of theinspection sample is multi-directionally condensed, and the condensedscattered light is photoelectrically converted to inspect a defect whichexists on the surface of the inspection sample. The apparatus includesfirst plural photoelectric conversion elements for performing amulti-directional detection, and second plural photoelectric conversionelements for performing the multi-directional detection. The firstplural photoelectric conversion elements are arranged each at a firstelevation angle with respect to an inspection sample surface, and thesecond plural photoelectric conversion elements are arranged each at asecond elevation angle higher than the first elevation angle.

According to the third aspect of the structure, in a surface defectinspection apparatus, a laser beam focused on a surface of an inspectionsample is irradiated, a scattered light generated on the surface of theinspection sample is multi-directionally condensed, and the condensedscattered light is photoelectrically converted to inspect a defect whichexists on the surface of the inspection sample. The apparatus includesfirst plural photoelectric conversion elements for performing amulti-directional detection, and second plural photoelectric conversionelements for performing the multi-directional detection. The firstplural photoelectric conversion elements are arranged each at a firstelevation angle with respect to an inspection sample surface, the secondplural photoelectric conversion elements are arranged each at a secondelevation angle higher than the first elevation angle, and sensitivityof the first and the second plural photoelectric conversion elements isindividually adjusted.

According to the fourth aspect of the structure, in a surface defectinspection apparatus, a laser beam focused on a surface of an inspectionsample is irradiated, a scattered light generated on the surface of theinspection sample is multi-directionally condensed, and the condensedscattered light is photoelectrically converted to inspect a defect whichexists on the surface of the inspection sample. The apparatus includesfirst plural photoelectric conversion elements for performing amulti-directional detection, and second plural photoelectric conversionelements for performing the multi-directional detection. The firstplural photoelectric conversion elements are arranged each at a firstelevation angle with respect to an inspection sample surface, and thesecond plural photoelectric conversion elements are arranged each at asecond elevation angle higher than the first elevation angle. The firstand the second plural photoelectric conversion elements are allowed toset the threshold value capable of distinguishing the detection signal,that is, noise from the defect signal based on the level of the shotnoise caused by the photoelectric conversion element.

Another problem to be solved by the present invention will be described.Recently, the LSI wiring has been rapidly miniaturized to cause the sizeof the defect to be detected in the optical inspection to approach thelimit of detection. According to the semiconductor roadmap, in the year2007, the mass production of the LSI of 65 nm node has reportedly beenabout to start. The production requires the performance for detectingthe defect with the size half the DRAM ½ pitch.

It is known that the scattered light intensity I upon the laserirradiation to the defect establishes the relationship of I∝d̂6 (d:particle size of the defect). That is, as the defect size becomessmaller, the generated scattered light is rapidly reduced. The processfor reducing the illumination wavelength, increasing the output of thelaser, reducing the laser beam spot may be employed for intensifying thegenerated scattered light. The improvement in the detection sensitivityby reducing the wavelength will be described. Assuming that theillumination wavelength is set to λ, the scattered light intensity Iestablishes the relationship of I∝λ̂(−4). In other words, the generatedscattered light may be intensified by reducing the illuminationwavelength, which is effective for improving the detection sensitivity.However, reduction of the illumination wavelength generally increasesthe absorbing coefficient of the substance, thus increasing the rate ofthe temperature rise on the sample surface.

The improvement in the detection sensitivity by increasing the laseroutput will be described. The scattered light intensity is substantiallyproportional to the laser output. So the scattered light may beintensified by making the laser output high. Likewise the case forreducing the illumination wavelength, the rate of the temperature riseon the sample surface may be increased. As a result, further improvementin the detection sensitivity to exceed the current level by increasingthe output cannot be expected.

The improvement in the detection sensitivity by reducing theillumination spot will be described. Reduction in the illumination spotmay reduce the scattered light intensity from the wafer roughness (tinysurface roughness). The detection sensitivity may be improved in view ofthe noise reduction. However, the laser irradiation per unit area isincreased by the reduced beam spot, thus increasing the rate of thetemperature rise on the sample surface.

It is difficult for a mere extension of the generally employed processto further improve the detection sensitivity as the sample is damaged bythe temperature rise. It is therefore an object of the present inventionto provide the surface defect inspection method and the surface defectinspection apparatus for improving the detection sensitivity whilesuppressing the temperature rise on the sample surface.

In the present invention, the sample is subjected to a line illuminationto increase the beam spot length to the feed pitch of the stage suchthat substantially the same region of the inspection sample isilluminated plural times in the single inspection to add the resultantplural scattered lights for improving the detection sensitivity.

The line illumination may increase the state where two or more defectsexist simultaneously in the illumination range. In the aforementionedcase, the sensor with the plural pixels may be used for dividing theillumination range so as to individually detect the defects in therespective ranges.

The plural scattered lights resulting from the single inspection aresubjected to the appropriate processing such as the amplification andthe noise elimination by the analog circuit. Then the scattered lightsgenerated from substantially the same region of the inspection sampleare added in the signal processor to improve the sensitivity of thedefect detection.

The summary of the present invention for solving the aforementionedproblems will be described hereinafter.

(1) A surface defect inspection method includes a step of irradiating alaser beam to the same region on the sample surface plural times, a stepof detecting each scattered light from the same region individually, anda step of adding or averaging the detected plural signals. The defectdetermination is performed based on the added or the averaged signal.The detection sensitivity may be improved while suppressing thetemperature rise on the sample surface.

(2) In the step of irradiating the laser beam to the same region on thesample surface plural times of the surface defect inspection, the lineillumination of the laser beam on the sample surface is performed, andthe line illumination region is moved in the longitudinal direction atthe pitch shorter than the length of the line illumination region in thelongitudinal direction. As a result, the irradiation to the same regionis performed plural times. This makes it possible to perform irradiationand detection to the same region plural times while maintaining the goodthroughput, thus improving the detection sensitivity.

(3) A surface defect inspection apparatus includes a stage which holdsthe sample, an illumination optical system for linearly irradiating thelaser beam to the illumination region on the sample surface, and adetection optical system for detecting the scattered light from the lineillumination region on the sample surface. The stage is moved in thelongitudinal direction of the line illumination region on the samplesurface at the feed pitch shorter than the longitudinal length of theline illumination region.

(4) The surface defect inspection apparatus for inspecting the sampleincludes a stage which holds the sample, an illumination optical systemfor irradiating the plural divided laser beams in array to the samplesurface, and a detection optical system for detecting the scatteredlight from the plural illumination regions on the sample surface. Thestage moves in the longitudinal direction of the line illuminationregion on the sample surface at the feed pitch shorter than thelongitudinal length of the line illumination region.

These and other objects, features and advantages of the invention willbe apparent from the following more particular description of preferredembodiments of the invention, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an embodiment (side view) of the presentinvention;

FIG. 2 is a view showing an embodiment (plan view) of the presentinvention;

FIG. 3 is a view showing an embodiment (plan view) of the presentinvention;

FIG. 4 is an explanatory view of a signal processing circuit;

FIG. 5 is an explanatory view of a signal processing circuit;

FIG. 6 is a view representing the intensity distribution of thescattered light from the tiny defect;

FIG. 7 is an explanatory view of a signal processing circuit;

FIG. 8 is an explanatory view of the process for adjusting thesensitivity of the photomultiplier tube;

FIG. 9 is an explanatory view of the process for setting the thresholdvalue;

FIG. 10 is an explanatory view with respect to the process shown in FIG.9;

FIG. 11 is an explanatory view of the inspection flow;

FIG. 12 is an explanatory view showing an example of GUI;

FIG. 13 is an explanatory view of the defect classification processingcircuit;

FIG. 14 is an explanatory view of the defect classification;

FIG. 15 is a view schematically showing the structure of the inspectionapparatus according to the present invention;

FIG. 16 is an explanatory view which shows the imaging system in detail;

FIG. 17 is a view schematically showing the illumination optical systemand the detection optical system which exist at different elevationangles;

FIG. 18 is a view schematically showing the detection optical systemseach in the different azimuth direction;

FIG. 19 is an explanatory view representing the inspection method forperforming the illumination to the same defect plural times;

FIG. 20 is an explanatory view of the definition of SN ratio;

FIG. 21 is an explanatory view representing the detection of thescattered light from the defect in separated way using the photodiodearray when plural defects exist on the beam spot;

FIG. 22 is an explanatory view showing the relationship between theposition through which the defect passes and the generated scatteredlight intensity when the illumination intensity distribution is Gaussiandistribution;

FIG. 23 is an explanatory view showing the relationship between theposition through which the defect passes and the generated scatteredlight intensity when the illumination intensity distribution is uniform;

FIG. 24 is an explanatory view of the illumination optical system fordividing the laser beam from the single light source into pluralsections, and performing the long illumination by arraying thosesections in the radial direction;

FIGS. 25A and 25B show the process for adding the signals when thephotodiode array is employed in the detection optical systems disposedin the plural azimuth directions;

FIGS. 26A and 26B show the process for adding the signal when thephotodiode array and PMT are employed in the detection optical systemsdisposed in the plural azimuth directions;

FIGS. 27A and 27B show the detection light intensity when thesensitivity of the light receiving section is different;

FIGS. 28A and 28B show the process for correcting the sensor sensitivitybased on the detection information prior to the rotation;

FIG. 29 is an explanatory view representing the coordinate merge processof the signal detected plural times with respect to the same defect;

FIGS. 30A and 30B show the difference between the generally employedscanning method and the scanning method according to the presentinvention;

FIG. 31 is a flowchart showing the process for detecting the defect inthe inspection apparatus; and

FIG. 32 is a view showing an example of GUI.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described.

FIGS. 1 to 3 show an example of an apparatus for detecting thedefect/foreign matter on the semiconductor wafer before forming thecircuit pattern. FIG. 1 is a side view, FIG. 2 is a plan view of a lowangle detection system, and FIG. 3 is a plan view of a high angledetection system. The apparatus shown in FIG. 1 includes an illuminationoptical system 101, a detection optical system 102 and a wafer stage103. The illumination optical system 101 includes a laser light source2, an attenuator 3, a beam expander 4, wavelength plates 5, 6, and acondensing lens 8.

The laser beam from the laser light source 2 has its light intensityadjusted to the required value by the attenuator 3. The beam radius ofthe laser is expanded by the beam expander 4, and the polarizationdirection of the illumination is set by the wavelength plates 5, 6. Thecondensing lens 8 performs condensing and illumination to the detectionarea on a wafer 1. Mirrors 7 a, 7 b are employed for changing theillumination optical path when required. The wavelength plates 5 and 6are employed to set the polarization of the illumination to Spolarization, P polarization and circular polarization. Preferably theillumination elevation angle θi ranges from 5° to 25°.

The attenuator 3 includes a half-wave plate and a polarization beamsplitter. The polarized angle of the beam from the laser light source(linear polarization) is inclined by the half-wave plate to change theintensity of light passing through the PBS (Polarized Beam Splitter). Asthe half-wave plate rotates, the polarized axis is changed to adjust thelight intensity.

The detection optical system 102 includes a low angle detection systemand a high angle detection system formed of scattered light detectionlenses 9 a, 9 c, 12 a, 12 c, analyzers 10 a, 10 c, 13 a, 13 c, andphotoelectric conversion elements 11 a, 11 c, 14 a, 14 c, respectivelysuch that the scattered light from the foreign matter/defect on thedetection area is substantially condensed on the light receivingsurfaces of the photoelectric conversion elements 11, 14 by thescattered light detection lenses 9, 12. Each of the photoelectricconversion elements 11, 14 generates an electric signal in proportion tothe received scattered light intensity so as to be processed in thesignal processing circuit (not shown). As a result, the foreignmatter/defect is detected to obtain such information as the size andlocation.

The photoelectric conversion elements 11, 14, for example, the TVcamera, the CCD linear sensor, the TDI sensor and the photomultipliertube, receive the scattered light condensed by the detection opticalsystem 102 so as to be photoelectrically converted. The analyzers 10, 13are employed for detecting only the component in the specific directioncontained in the scattered light. Preferably, the detection elevationangle (center angle) θ₁ of the low angle detection system is set to thevalue ranging from 15° to 35°, and the detection elevation angle (centerangle) θ₂ of the high-angle detection system is set to the value rangingfrom 45° to 70°

The wafer stage 103 includes a chuck 15 for holding the wafer 1, arotating mechanism 17 for rotating the wafer 1, and a direct feedmechanism 16 for directly feeding the wafer 1 in the radial direction.The wafer 1 is subjected to the rotation scanning and the direct feedmovement in the horizontal direction by the wafer stage 103 to allow thedetection of the foreign matter/defect in the entire region of the wafer1 and classification of the defect.

FIG. 2 is a plan view of the low angle detection system, which allowsthe multi-directional detection. In FIG. 2, 9 a-9 f denote scatteredlight detection lenses, 10 a-10 f denote analyzers, 11 a-11 f denotephotoelectric conversion elements. The embodiment allows the 6-directiondetection. Each output of the respective photoelectric conversionelements 11 is subjected to such calculation as addition, subtraction,and division in accordance with the usage. Preferably each detectionazimuth (center angle) is set to 20° to 50° (φ₁), −20° to −50° (φ₂), 70°to 110° (φ₃), −70° to 110° (φ₄), 130° to 160° (φ₅), and −130° to −160°(φ₆) with respect to the illumination direction, respectively.

FIG. 3 is a plan view of the high angle detection system similar to theone shown in FIG. 2, which allows the multidirectional detection. InFIG. 3, 12 a-12 d denote scattered light detection lenses, 13 a-13 ddenote analyzers, 14 a-14 d denote photoelectric conversion elements.The embodiment allows the 4-direction detection. Each output of therespective photoelectric conversion elements 14 is subjected to suchcalculation as addition, subtraction, and division in accordance withthe usage. Preferably each detection azimuth (center angle) is set to±10° (φ₇), 80° to 110°(φ₈), −80° to −110° (φ₉), and 180°±10° (φ₁₀) withrespect to the illumination direction, respectively.

FIG. 4 shows an example of the signal processing performed in the lowangle detection system which employs the photomultiplier tube as thephotoelectric conversion element 11. The photomultiplier tube 11 a-11 frequires application of the high voltage supplied from a high voltage DCpower source 19. The output of the photomultiplier tube 11 is subjectedto the current-voltage conversion and the required voltage amplificationby the amplifier circuit 18 a-f, which is then added by an adder circuit20. At this time, the amplifier circuit 18 adjusts the amplificationfactor for correcting the difference in sensitivity of thephotomultiplier tube 11.

The output of the adder circuit 20 has the DC component and theunnecessary noise eliminated by the band-pass filter 21 so as to besubjected to the digital conversion by an AD conversion circuit 22. Theoutput of the AD conversion circuit 22 is compared with a thresholdvalue by a comparison circuit 23. When the output exceeds the thresholdvalue, the AD conversion value and the R·θ coordinate are loaded in adefect memory 26. The threshold value is set to a latch 24 from the CPU(not shown) via an interface 25. The content of the defect memory 26 isread from the CPU (not shown) so as to be used for displaying the defectmap and classifying the defect. FIG. 5 shows an example of the signalprocessing in the high angle detection system, the content of which isthe same as the one shown in FIG. 4.

In FIG. 5, 14 a-14 d denote photoelectric conversion elements, 27 a-27 ddenote the amplifier circuits, 28 denotes an adder circuit, 29 denotesthe band-pass filter, 30 denotes an AD conversion circuit, 31 denotes acomparison circuit, 32 denotes a latch, 33 denotes an interface, 34denotes the defect memory.

FIG. 6 shows an example of a scattered light intensity distribution 35which is caused by the tiny defect upon illumination with the Ppolarization. When the dimension of the defect is approximately ⅕ of theillumination wavelength or shorter, the scattered light intensitydistribution becomes isotropic as shown in FIG. 6. In this case, therespective detection signals become substantially the same value (S). Ashot noise (N) occurs upon the photoelectric conversion in thephotomultiplier tube 11.

The shot noise (N) output from each photomultiplier tube 11 is random,and the SN ratio of the output signal from the photomultiplier tube 11becomes S/N. Referring to FIGS. 4 and 5, when all the detection signalsare added and averaged, the shot noise is averaged to become 1/16. Thenthe S/N ratio of the detection signal is increased by 16 times. Eachindividual processing for the photomultiplier tube 11 makes it possibleto detect the tiny defect. When the addition/averaging is performed inthe case where the scattered light intensity distribution is biased likescratch to be detected only in the single photomultiplier tube 11, thedetection signal becomes ⅙, and the shot noise becomes 1/√6, thusreducing the S/N ratio to 1/√6 compared with the process for each of thephotomultiplier tube 11 individually.

In order to avoid the aforementioned disadvantage, a first embodiment isprovided as shown in FIG. 7. The circuit which is the same as theprocessing circuit shown in FIG. 4 is added for each of thephotomultiplier tubes 11 a-11 f. In FIG. 7, 18 a-18 f denote theamplifier circuits, 21 a-21 f denote the band-pass filter, 22 a-22 fdenote an AD conversion circuit, 24 a-24 f denote latches. The output ofthe comparison circuit 23 a-23 f are subjected to the logic ORoperation. When any one of the value exceeds the threshold value, theoutputs of the all the AD conversion circuits 22 and the R·θ coordinateare loaded in the defect memory 26. This makes it possible to preventthe error failing to detect the anisotropic defect with thedirectionality in the scattered light intensity distribution.

FIG. 8 shows an embodiment for correcting the difference in sensitivityof the photomultiplier tube 11 a-11 f. A power unit 39 a-39 f arestructured to adjust the high application voltage in accordance with theinput voltage. The power unit of the type of C4900 produced by HamamatsuPhotonics may be employed as one of the exemplary power units. Thevoltage value is written into the latch 37 a-37 f via the interface 40to convert the value into the voltage value by the DA conversion circuit38 a-38 f so as to be applied to the power unit 39 a-39 f. This makes itpossible to supply the high application voltage to the photomultipliertube 11. The change in the voltage value written into the latch 37 a-37f allows the sensitivity of the photomultiplier tube 11 to be adjustedfrom the CPU. The adjustment of the amplification factor by theamplification circuit 18 a-18 f may be performed together with theaforementioned operation to allow the easy correction of the differencein the sensitivity.

The intensity and distribution of the scattered light on the wafersurface varies depending on the space frequency/degree of the roughnessthereon. When the scattered light intensity on the wafer surfacedetected by the photomultiplier tube 11 a-aaf are set to Su, the shotnoise generated thereby becomes √Su. In the case where the scatteredlight intensity on the wafer surface detected by the photomultipliertube 11 a-11 f vary depending on each of the photomultiplier tubes 11a-11 f, the resultant shot noise will vary. It is necessary to changethe threshold value for detecting the defect. An embodiment to cope withthe aforementioned problem and the detailed process will be describedreferring to FIGS. 9 and 10, respectively.

In FIGS. 9 and 10, an output signal 45 a from the amplifier circuit 18 ais separated into a wafer signal 46 a and a defect signal 47 a whichcontains the shot noise using the band-pass filter 21 a and the lowpassfilter 41 a. The wafer signal 46 a which has passed through the lowpassfilter 41 a is used for setting the threshold value. The signal derivedfrom the wafer signal 46 a is subjected to the digital signal conversionby the AD conversion circuit 42 a, and is formed into the thresholdvalue Vth by the calculation circuit 43 a so as to be set in the latch44 a. The shot noise 47 a is subject to the digital conversion by the ADcon version circuit 22 a, and is sent to a comparison circuit 23 a. Thewafer signal also is sent to the comparison circuit 23 a. The shot noiseis proportional to the square root of the wafer signal Su, and thethreshold value Vth is calculated through the following equation (1):

Vth=k·√(Su·Δf)

where k denotes the constant and Δf denotes a frequency band of thecircuit. In FIG. 10, left side graph shows the out put signal 45 a, inwhich y-axis Vo denotes output signal, and x-axis denotes time (t).Upper right side graph shows the wafer signal 46 a, in which y-axis Vndenotes wafer signal, and x-axis denotes time (t). Lower right sidegraph shows the defect signal 47 a, in which y-axis Vs denotes defectsignal, x-axis denotes time (t).

FIG. 11 shows an example of the inspection routine. The inspectionrecipe is loaded to set the required parameter in the apparatus. Thewafer is loaded and inspected to input the defect data from the defectmemory. When the inspection ends, the wafer scan (rotation and thesingle axis feed) is stopped so as to unload the wafer. Thereafter, thedefect map is displayed on the GUI screen as required.

FIG. 12 shows an example of the GUI. A GUI screen 48 includes at least adefect map 49 displayed after the end of the inspection, and a defectmap display sensor selector screen 50.

FIG. 13 shows an example of distinguishing the defect. The detectionsignal V_(L) of the low angle detection system flows from Ad conversioncircuit 22, and the detection signal V_(H) of the high angle detectionsystem flows from Ad conversion circuit 30. The ratio of the detectionsignal V_(L) of the low angle detection system to the detection signalV_(H) of the high angle detection system is calculated by a processingcircuit 51, and the calculation result is written into the defectmemory. The detailed process will be described referring to FIG. 14. Thecalculation results are plotted on the graph having an x-axis as V_(L)and the y-axis as V_(H). On the graph, the concave defect (COP, scratchand the like) is observed in an area 53 above the threshold curve 52,and the convex defect is observed in an area 54 below the thresholdcurve 52. The threshold curve 52 is set to allow the appropriatedistinguishing between the concave defect and the convex defect (defecttype).

Referring to FIG. 14, each of the defects in the area below the dottedline 52 is the convex defect, and each of the defects in the area abovethe dotted line 52 is the concave defect. In most of the cases, theconcave defect has been existed in the Si wafer, and the convex defectis likely to be caused in the apparatus. The number of the convexdefects larger than that of the concave defects in spite of the samedefect density tends to indicate the problem in the manufacturingapparatus.

The above explanation has been made when the photomultiplier tube 11 isused as the photoelectric conversion element. However, the relationshipbetween the shot noise and the defect detection signal is kept unchangedwhen the CCD is used as the photoelectric conversion element.Accordingly, the aforementioned description is applicable to the casewhere the element other than the photomultiplier tube 11 is used as thephotoelectric conversion element.

The detection signals of the multi-directionally detected scatteredlights are added to detect the tiny defect, and to prevent the errorfailing to detect the anisotropic defect by performing the individualprocess for each of the detection signals.

The obtained defect data are automatically analyzed to make adetermination whether the defect has been caused by the problem of theapparatus, or it has already existed on the substrate.

An example of the embodiment according to the invention for solving theaforementioned problem will be described referring to FIG. 15. FIG. 15schematically shows the structure including an illumination opticalsystem 2-101, a detection optical system 2-102, a wafer stage 2-103, anda circuit/signal processor. The illumination optical system 2-101includes a laser light source 2-2, a beam expander 2-3, a homogenizer2-4, mirrors 2-5, 2-6, and a cylindrical lens 2-7. A laser beam 2-100irradiated from the laser light source 2-2 allows the beam radius to beadjusted to the required size by the beam expander 2-3, and converted bythe homogenizer 2-4 into the uniform illumination distribution. It isfurther subjected to the line illumination in the inspected region onthe wafer 2-1 by the cylindrical lens 2-7.

The laser light source for generating ultraviolet or extra ultravioletlaser beams may be employed as the laser light source 2.

The homogenizer 2-4 is used for making the illumination intensityuniform. However, the diffraction optical element and the fly eye lensmay be used to make the illumination intensity uniform. The illuminationmay be performed without using the homogenizer 2-4. The illuminationwithout using the homogenizer suppresses the attenuation of the laserbeam intensity, thus allowing the illumination with the high intensity.

The cylindrical lens 2-7 is used for the line illumination. However, theanamorphic optical system formed of plural prisms may be used to changethe beam radius on the plane perpendicular to the optical axis withrespect to only one direction such that the condensing lens is used forthe line illumination to the sample. The use of the anamorphic opticalsystem is effective in view of easy adjustment of the optical axis.

The detection optical system 2-102 includes an imaging system 2-8 and aphotodiode array 2-9. FIG. 16 illustrates the detection optical system2-102 in detail. The detection optical system 2-102 includes acondensing lens 2-21, an image intensifier 2-22, an imaging lens 2-23and a photodiode array 2-9. The light scattered from the beam spot 2-20is condensed by the condensing lens 2-21. The scattered light isamplified by the image intensifier 2-22 so as to be imaged on thephotodiode array 2-9 through the imaging lens 2-23.

The image intensifier 2-22 is used for amplifying the weak scatteredlight to be detectable. However, instead of the image intensifier, thesensor with high gain, for example, EM-CCD, the multi-anode PMT and thelike may be employed. The use of the aforementioned sensor is effectivein view of downsizing the apparatus.

The photodiode array 2-9 is used for receiving the scattered light to bephotoelectrically converted. However, TV camera, CCD linear sensor, TDI,photodiode array, multi-anode PMT, and the like may be employed. Forexample, the use of the 2D sensor allows the wide region to be inspectedat one time.

The photodiode array 2-9 generates the electric signal corresponding tothe received light intensity so as to be subjected to the requiredprocess by the analog circuit 2-51 including amplification, noiseprocess, and analog-digital conversion. The signal processor 2-52 addsplural optical signals scattered from substantially the same region andperforms the defect determination to display the defect map by the mapoutput section 2-54 via a CPU 2-53.

The wafer stage 2-103 is formed of a chuck (not shown) for holding thewafer 2-1, a rotating stage 2-10 for rotating the wafer, and a parallelstage 2-11 for moving the wafer in the radial direction. The wafer stage2-103 performs the rotation scan and the parallel scan to spirallyilluminate the entire sample surface. The stage control section 2-55controls the rotating speed and the parallel advancing speed so as toilluminate the desired region.

As a feature of the present invention, the line illumination isperformed to the sample surface, and the sample is moved insubstantially the same direction as the longitudinal direction ofillumination while being rotated. As a result, the entire sample surfacemay be spirally illuminated to allow the surface defect inspection basedon the detected scattered light.

FIG. 15 shows the example where the single illumination optical systemand the single detection optical system are employed. However, pluralillumination optical systems and detection optical systems may beemployed likewise the case shown in FIG. 17 including an obliqueillumination optical system 2-101 a for illuminating the sample from thelow elevation angle, a perpendicular illumination optical system 2-101 bfor illuminating the sample from substantially the perpendiculardirection, a low angle detection optical system 2-102 a for detectingthe sample at the low elevation angle, and a high angle detectionoptical system 2-102 b for detecting the ample at the higher elevationangle compared with the low angle detection optical system.

The oblique illumination optical system 2-101 a includes the laser lightsource 2-2, the beam expander 2-3, the homogenizer 2-4, the mirrors 2-5,2-6 a, and a cylindrical lens 2-7 a. Likewise, the perpendicularillumination optical system 2-101 b includes the laser light source 2-2,the beam expander 2-3, the homogenizer 2-4, a mirror 2-6 b, and acylindrical lens 2-7 b. The aforementioned structures allow any of thecomponents of the embodiment shown in FIG. 15 to be omitted andreplaced.

In this case, the mirror 2-5 is structured to change the advancingdirection of the laser beam 2-100, and the optical system is switchablebetween the oblique illumination optical system 2-101 a and theperpendicular illumination optical system 2-102 b in need.

The oblique illumination optical system may be selected to improve thedetection sensitivity, and the perpendicular illumination optical systemis selected to improve the capability of classifying the defect.Accordingly, the desired system may be selected depending on the usage.

The low angle detection optical system 2-102 a includes an imagingsystem 2-8 a and a photodiode array 2-9 a. Likewise, the high angledetection optical system 2-102 b includes an imaging system 2-8 b and aphotodiode array 2-9 b. The imaging system 2-8 a includes the condensinglens, the image intensifier, and the imaging lens (not shown). Theimaging system 2-8 b has the same structure. The aforementionedstructures allow any of the components of the embodiment shown in FIG.15 to be omitted and replaced.

Each of the photodiode arrays 2-9 a and 2-9 b generates the electricsignal corresponding to the received light intensity so as to besubjected to the required process by the analog circuits 2-51 a and 2-51b including amplification, noise process, and analog-digital conversion.Then the signal processor 2-52 adds the plural optical signals scatteredfrom substantially the same region, and performs the defectdetermination such that the defect map is displayed by the map outputsection 2-54 via the CPU 2-53.

In the embodiment, substantially the same location is detected at thedifferent elevation angle at substantially the same time. Any of theoptical system selected from the low angle detection optical system andthe high angle detection optical system may be used for the inspectionby adjusting the sensitivity of the respective sensors such that thedynamic range of the detected particle size is widened.

The use of the combination of the illumination optical system and thedetection optical system makes it possible to improve the accuracy inthe defect classification. For example, as for the convex defect, thelow angle detection optical system is capable of detecting the largescattered light upon the oblique illumination. As for the concavedefect, the high angle detection optical system is capable of detectingthe large scattered light upon the perpendicular illumination.

Referring to FIG. 17, the example where the detection optical systemsexist in the different elevation angle directions. However, pluraldetection optical systems may be provided in the different azimuthdirections as shown in FIG. 18. FIG. 18 is a view of the embodimentaccording to the present invention when seen from above, which shows awafer 2-1, the illumination optical system 2-101, and detection opticalsystems 2-102 c to 2-102 h. The detection optical systems 2-102 c to2-102 h are formed of the corresponding imaging systems 2-8 c to 2-8 h,and the respective photodiode arrays 2-9 c to 2-9 h. The detectionsignal is subjected to the required process by the analog circuitincluding amplification, noise processing and analog-digital conversion.The signal processor adds the plural optical signals scattered fromsubstantially the same region and performs the defect determination.Then the defect map (not shown) is displayed by the map output sectionvia the CPU. With respect to the structure of the detection opticalsystem, each of the imaging systems 2-8 c to 2-8 h is formed of thecondensing lens, the image intensifier, and the imaging lens (notshown), respectively.

The use of the detection optical system which exists at plural azimuthsallows the detection optical system capable of detecting more scatteredlights from the defect while suppressing the noise to be selected byperforming the inspection when the angular property of the scatteredlight caused by the size/configuration of the defect, film type of thesample, and surface roughness. This makes it possible to improve thedetection sensitivity.

Referring to FIG. 18, six detection optical systems are arranged indifferent azimuth directions. However, the number of the detectionoptical systems does not have to be limited to six, but may bearbitrarily set to be arranged in the arbitral azimuth direction. Theplural detection optical systems do not have to be arranged atsubstantially the same elevation angle. Furthermore, the detector doesnot have to be arranged in substantially the same azimuth direction.

In the present invention, the line illumination and the scanning allowthe illumination to the same defect plural times. The generally employedinspection method will be described first, and then the inspectionmethod according to the present invention will be described hereinafter.

The stage advances in parallel at substantially the constant speed inthe radial direction (R direction) while rotating. It is assumed thatthe advancing distance in the radial direction in the cycle of thesingle rotation is referred to as the feed pitch. The rotation/paralleladvancement allows the spiral scan on the entire sample surface.However, the length of the beam spot in the radial direction issubstantially the same as the feed pitch length. In most of the case,the illumination to the single defect is performed only once.

In the present invention, the line illumination is performed, and thebeam spot length is made longer than the pitch length to illuminate thesame defect plural times.

Referring to FIG. 19, the defect 2-25 is illuminated four times in thecondition where the length of the beam spot 2-20 is four times longerthan that of the feed pitch 2-26. The illumination performed pluraltimes will be described referring to FIG. 19. At a time point t1, thefirst illumination is performed to the defect 2-25. At a time point t2,the wafer rotates at the single round. The beam spot advances in theradial direction by the distance substantially corresponding to the feedpitch 2-26 to illuminate the defect 2-25 again. Then at the time pointst3 and t4, the wafer rotates at the single round, respectively toilluminate the defect 2-25. Referring to FIG. 19, the defect 2-25 may beilluminated four times, and the detected light is added by the analogcircuit or the signal processor. The number of times for illumination isnot limited to four, but may be arbitrarily set so long as it is pluraltimes.

The improvement in the detection sensitivity by adding the pluralscattered lights in the present invention will be described.

The improvement in the detection sensitivity will be described inreference to the SN ratio defined in FIG. 20. Referring to FIG. 20, they-axis of the graph denotes the detected light intensity, and x-axisdenotes the time (t). The sample surface is constantly illuminated evenif no defect exists on the beam spot so as to continuously detect thescattered light 2-30 generated in accordance with each size of concavityand convexity of the wafer roughness. Assuming that the averageintensity of the scattered lights from the wafer roughness is set to N₀,the detected light intensity fluctuates at the amplitude of √N₀ owing tofluctuation on the sensor light receiving surface caused by thephotoelectric conversion, thus generating the noise. The defect whichexists on the beam spot generates the scattered light 2-31. Assumingthat the intensity of the scattered light from the defect is set to S₀having the value N₀ as the standard, the SN ratio is defined as“S₀/√N₀”.

The scattered light from the same defect is added n times to increasethe scattered light intensity from the defect from S₀ to n×S₀, and thescattered light intensity from the wafer roughness from N₀ to n×N₀. Thatis, the SN ratio becomes “n×S₀/√(n×N₀)”, and the detection sensitivityis intensified by √n times.

It is effective to illuminate the same defect plural times by increasingthe beam spot to be longer than the feed pitch, that is, generating theline illumination. Instead of increasing the beam spot length, the feedpitch length may be decreased to allow the same defect to be illuminatedplural times. In this case, however, the throughput is reduced.

Referring to FIG. 21, the photodiode array is used to divide the beamspot to be detected such that each scattered light from the two or moresimultaneously illuminated defects may be detected individually. Thephotodiode array having four light receiving sections 2-35 a, 2-35 b,2-35 c, and 2-35 d will be described.

When the defects 2-25 a and 2-25 b are simultaneously illuminated on thebeam spot 2-20, they may be divided by the imaging system 2-8 withrespect to the light receiving sections 2-35 a and 2-35 d of thephotodiode array 2-9. The divided beam spot is detected to allow thenoise from the wafer roughness to be reduced, resulting in the effectexpected to improve the detection sensitivity.

In the inspection method according to the present invention, thesubstantially the same region is illuminated with the line illuminationplural times, and the plural scattered lights are added to improve thedetection sensitivity. The detection sensitivity may be improved withoutdecreasing the illumination wavelength to be short, or without using theprocess for increasing the laser output and reducing the beam spot. Thatis, the embodiment of the present invention is capable of improving thedetection sensitivity while suppressing the damage to the sample.

In the illumination optical system, the laser beam intensitydistribution generally has a Gaussian distribution. In the presentinvention, however, the illumination may be performed with the uniformintensity distribution.

In the case where the intensity distribution of the beam spot 2-20 a hasa Gaussian distribution 2-40 a as shown in FIG. 22, the scattered light2-41 a is generated by illuminating the defect 2-25 a on the beam spot2-20 a, and the scattered light 2-41 b which is larger than thescattered light 2-41 a is generated by illuminating the defect 2-25 b.In the right side drawing of FIG. 22, y-axis is detected lightintensity, and x-axis is time (t). In the case where the intensitydistribution of the beam spot 2-20 b has the uniform distribution 2-40 bon the beam spot 2-20 b as shown in FIG. 23, the scattered light 2-41 cresulting from illumination to either the defect 2-25 a or 2-25 b on thebeam spot 2-20 b has substantially the same size. In the right sidedrawing of FIG. 23, y-axis is detected light intensity, and x-axis istime (t).

The wafer stage which is rotated at high speeds during the inspectiongenerates oscillation both in height and radial directions. So thefluctuation in the sample height and heave occur at high frequency.There may be often the case where the positional relationship betweenthe defect and the beam spot displaces. However, the fluctuation in thedetected scattered light intensity resulting from the displacement ofthe illumination position may be suppressed by allowing the illuminationintensity to have the uniform distribution. This makes it possible toimprove the repeatability and stability with respect to the defectdetection sensitivity and coordinate accuracy.

In the illumination optical system, the line illumination is performedusing the beam expander and the cylindrical lens. However, the Wallastonprism may be used to divide the laser beam so that the divided laserbeams are arrayed in the radial direction for illumination, thus makingthe beam spot long enough to illuminate the sample surface.

The process for dividing the laser beam will be described referring toFIG. 24. Generally, the laser beam 2-100 from the laser light source 2is linearly-polarized. After passing through the beam expander 2-3 andthe homogenizer 2-4, the laser beam is circularly polarized by thequarter-wave plate 2-42 a so as to be divided into twolinearly-polarized beams which is orthogonal with each other at theWallaston prism 2-43. The divided laser beam is circularly polarized bythe quarter-wave plate 2-42 b again such that the sample surface isilluminated by the condensing lens 2-44 on the beam spots 2-20 c and2-20 d. In this way, the long beam spot may be generated by illuminatingthe sample on the plural arrayed beam spots.

The distance between the thus divided two beam spots may be arbitrarilyadjusted, which allows the illumination by overlapping or separating thebeam. This makes it possible to adjust the number of illuminations tosubstantially the same region.

The intensity of the divided laser beam allows the adjustment of theellipticity of the circular polarization/azimuth of elliptic long axisby controlling the angle defined by the oscillating direction of thelinearly polarized laser beam 2-100 and the phase lag axis of thequarter-wave plate 2-42 a. Illumination intensity of the beam spots 2-20c and 2-20 d divided by the Wallaston prism 2-43 may be arbitrarilyadjusted by controlling the ellipticity/azimuth of elliptic long axis.This makes it possible to expand the dynamic range of the detectabledefect (to be described later). The beam spots 2-20 c and 2-20 d may beset to substantially the same intensity values or different intensityvalues.

In the embodiment shown in FIG. 24, the laser beam is divided into two.However, the laser beam may be divided into four, eight, or more byarranging plural combinations of the Wallaston prisms and thequarter-wave plates to the front of the quarter-wave plate 2-42 b andthe condensing lens 2-44. The illumination range may be adjusted bycontrolling each distance among the plural beam spots so as toarbitrarily adjust intensity of the plural laser beams.

The divided laser beams are arranged in substantially the same directionfor illuminating. However, the illumination may be performed in theoblique illumination optical system and the perpendicular illuminationoptical system simultaneously to array two beam spots. This makes itpossible to illuminate the same defect from substantially theperpendicular and oblique directions in the single inspection. The useof the difference in the detected elevation angle/detected azimuthdirection improves the defect classification performance

In the process for adding the scattered lights in the detection opticalsystem, an example of the detection optical systems in different azimuthdirections will be described. Referring to FIG. 25A, two detectionoptical systems, that is, 2-102 c and 2-102 d are provided.

FIG. 25B is an enlarged view showing the beam spot, the photodiode arraylight receiving section, and the analog circuit. The beam spot 2-20 isdivided and detected by the photodiode 2-9 c, and the detection signalsat the respective light receiving sections are amplified by thecorresponding circuits 2-45 a to 2-45 d for eliminating the noise.Likewise, the beam spot 2-20 is divided and detected by the photodiode2-9 d, and the detection signals at the respective light receivingsections are amplified by the corresponding circuits 2-46 a to 2-46 dfor eliminating the noise. In the adder sections 2-47 a to 2-47 d, theoutputs of the light receiving sections for detecting the scatteredlights from substantially the same region on the illuminated portion areadded. Outputs of the circuits 2-45 a and 2-46 a as signalscorresponding to substantially the same region on the illuminatedportion are added by the adder section 2-47 a. Likewise, the outputs ofthe circuits 2-45 b and 2-46 b, 2-45 c and 2-46 c, and 2-45 d and 2-46 das signals corresponding to substantially the same region on theilluminated portion are added by the adder sections 2-47 b to 2-47 drespectively for improving the detection sensitivity.

In the embodiment, four light receiving sections are employed for thephotodiode array. However, the number of the light receiving sections isnot limited, but may be arbitrarily set. The photodiode array 2-9 c doesnot have to have the same number of the light receiving sections as thatof the light receiving sections for the photodiode array 2-9 d. If thosephotodiode arrays use different number of the light receiving sections,signals of the light receiving sections which detect substantially thesame region are added.

The number of the detection optical system is not limited to two asdescribed herein. Plural detection optical systems may be provided inplural azimuth/elevation angle directions. If the plural detectionoptical systems exist, the signals of the light receiving sections whichdetect substantially the same region in the respective detection opticalsystems are added.

A method for adding the scattered light in the case where the detectionoptical systems exist in different azimuth directions will be describedtaking an example of the detection optical system using thephotomultiplier tube (PMT) as the sensor likewise the detection opticalsystem 2-104 shown in FIG. 26A. The detection optical system 2-104includes a condensing lens 2-60, a pin hole 2-61, and a PMT 2-62. Thedetection optical system 2-104 uses the pin hole 2-61 to reduce thedetection range so as to suppress the noise.

FIG. 26B is an enlarged view of the beam spot, the photodiode array, thePMT, and the analog circuit. The detection signal from the PMT 2-62 isamplified by the circuit 2-63 for eliminating the noise. As outputs ofthe circuits 2-63 and 2-45 c correspond to the signal in substantiallythe same region of the illuminated portion, the addition is performed bythe adder section 2-64 to improve the detection sensitivity. The signalsoutput from the circuits 2-45 a, 2-45 b, and 2-45 d are not added.

The PMT as the point sensor has the high response speed and small datacapacity. The PMT may be employed in the section where the highdetection sensitivity is not required, thus increasing the inspectionspeed.

The number of the detection optical systems is not limited to two.Plural systems may be provided in plural azimuth/elevation angledirections. The ratio of the detection optical system provided with thephotodiode array to the detection optical system provided with the PMTis not limited to 1:1. The azimuth at which the detection optical systemprovided with the photodiode array and the detection optical systemprovided with the PMT are arranged is not limited. Preferably, however,at least one of the photodiode arrays is disposed at the positionsubstantially in parallel with the illuminating direction.

In the inspection method according to the present invention, the samedefect is illuminated plural times. Upon the second illumination to thesame defect onward, the previous detection signal may be used forfeedback. The example for expanding the dynamic range by correcting thesensor sensitivity will be described.

FIGS. 27A and 27B are graphs each having the y-axis as the detectedlight intensity, and x-axis as the time. Referring to FIG. 27A, thedetected light intensity 2-70 is detected without being saturated.Referring to FIG. 27B, the detected light intensity 2-71 is saturated,thus failing to measure the accurate scattered light intensity. In FIGS.27A and 28B, x-axis is time (t). As the size determination in the defectdetermination is made based on the level of the detection lightintensity, it is important to detect the scattered light whilepreventing the saturation.

The process for preventing the saturation of the detection lightintensity will be described referring to FIGS. 28A and 28B. Thescattered light generated when the first illumination to the defect 2-25is performed on the bema spot 2-20 is detected by the light receivingsection 2-35 a and 2-35 c of the photodiode array 2-9 via the imagingsystem 2-8. When the resultant detected light intensity is saturated asshown in FIG. 27B, the second illumination is performed by lowering thesensor sensitivity. In the second illumination, the scattered light fromthe defect 2-25 is detected by the light receiving section 2-35 b of thephotodiode array 2-9 to allow the scattered light to be detected whilepreventing the saturation as shown in FIG. 27A.

The sensor sensitivity is corrected by changing the voltage applied tothe image intensifier and the multi-anode PMT, changing the sensorstorage time, performing the illumination at the changed illuminationintensity and the like. The sensor sensitivity may be corrected byadjusting the sensitivity during the inspection as needed. However, suchcorrection may be made by changing the sensitivity for each of the lightreceiving sections before starting the inspection, or using sensors eachhaving the different sensor sensitivity arrayed preliminarily. In thecase where the laser beam is divided by the Wallaston prism so as to bearrayed for illumination to allow each of the divided laser beams tohave the different intensity, the divided laser beams are arrayed togenerate the line illumination with different illumination intensitydistribution in the pseudo manner. This makes it possible to change thedetection sensitivity for each of the light receiving sections so as toperform the sensor sensitivity correction.

The process for adding the scattered lights by the signal processor willbe described referring to FIG. 29. The graph shown in FIG. 29 has they-axis as the R (radial) direction and the x-axis as θ (rotation)direction. Coordinates 2-112 a to 2-112 d represent detection of thesame defect. In the present invention, as the same defect is illuminatedplural times, the single defect is detected by the same number of timesas that of the illumination. For example, the defect coordinates 2-112a, 2-112 b, 2-112 c, and 2-112 d represent detections of the same defectduring the first, the second, the third and the fourth illuminations,respectively. Although the coordinates 2-112 a to 2-112 d represent thesame defect, the variation still exists because of errors caused by thefluctuation in the stage height and the illumination position for therespective illuminations. A predetermined region 2-111 is defined by thecoordinates 2-110 a, 2-110 b in the R direction and 2-110 c, 2-110 d inthe θ direction. When the signal detected in the predetermined region isdetermined as being the one from the same defect so as to be subjectedto the integrated processing. As an example of the integratedprocessing, each gravity center of the defect coordinates of 2-112 a to2-112 d is taken to set the final defect coordinate 2-113. Besides theuse of the gravity center coordinate as the final defect coordinate, theweighting may be performed so as to set the final defect coordinate. Thefluctuation in the coordinate which occurs for each detection isaveraged such that the improvement in the coordinate repeatability isexpected.

In the process for adding the scattered lights by the signal processor,the plural detected light intensities detected in the predeterminedregion 2-111 shown in FIG. 29 are added to set the final detected lightintensity, based on which the defect size is determined. Instead ofadding the plural detection light intensities to set the final detectionlight intensity, the average value of the plural detection lightintensities may be obtained to be set as the final detection lightintensity. If the detected light intensity value is large, the averagedetected light intensity is obtained rather than performing the addingto suppress the variation in the detected light intensity. This makes itpossible to improve the repeatability and stability for determining thedefect size. FIG. 29 shows the example where the defect is detected onlyfour times. However, the detection may be performed any number of times.

An example of the inspection method according to the present inventionwill be described referring to FIGS. 30A and 30B.

In the generally employed method, the spiral scanning is performed asshown in FIG. 30A. The sample inspection ends when the beam spot reachesthe most outer periphery. In the present invention, when the beam spotreaches the most outer periphery, the radial movement of the stage isstopped for performing the concentric scanning as shown in FIG. 30B.This makes it possible for the outer periphery to illuminatesubstantially the same region plural times likewise the inner periphery,thus preventing deterioration in the detection sensitivity on the outerperiphery.

The number of times for illumination on the outer periphery may bearbitrarily set for performing the concentric scanning. On the innerperiphery, the number of times for illumination to substantially thesame region is determined based on the relationship between the beamspot length and the feed pitch length. However, the number of times forilluminating the outer periphery does not have to be set to the samenumber of times for illuminating the inner periphery. It may beincreased to be larger than that for illuminating the inner periphery.

The routine for detecting the defect will be described referring to FIG.31. The recipe is set to determine the inspection conditions such as theillumination direction and the sensor sensitivity in step 2-120. Theprocess in step 2-120 includes the step of setting the processingperformed with respect to the beam spot length, the feed pitch and thedetected scattered light. The wafer scanning is started in step 2-121,and the detected scattered light is subjected to the signal processingset by the recipe in step 2-122. The defect determination is performedbased on the processed signal in step 2-123. Then the defect map isdisplayed in step 2-124.

FIG. 32 shows an example of the GUI which includes a defect map 2-130displayed after the end of the inspection, and a sub-window for settingthe inspection mode before starting the inspection. The defect map isdisplayed based on the defect signal loaded upon the inspection and thecoordinates. The inspection mode 2-131 may be selected through thedirect inputting or selection from the pull-down menu. The number oftimes for illuminating the same defect in the single inspection does nothave to be the same. For example, on the inner periphery of the sample,the inspection mode is selected to the standard mode (2-132), and on theouter periphery of the sample, the inspection mode is selected to thehigh sensitivity mode (2-133). In the high sensitivity mode, the feedpitch is decreased, and the number of times for illumination isincreased to improve the detection sensitivity.

In the embodiment of the present invention, the same defect isilluminated plural times in the single inspection, and the scatteredlights generated plural times are added to improve the detectionsensitivity. The use of the photodiode array with the plural pixelsallows the inspection without deteriorating the throughput. Theembodiment of the present invention provides the inspection method andthe inspection apparatus, realizing both the improvement in thedetection sensitivity and the increase in the throughput. Theinformation to be illuminated and detected plural times is used toexpand the dynamic range and to improve accuracy in the coordinate andthe defect size determination.

The defect inspection method and the defect inspection apparatus improvethe detection sensitivity while suppressing increase in the temperatureof the sample surface.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to be considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description and all changeswhich come within the meaning and range of equivalency of the claims aretherefore intended to be embraced therein.

What we claim is:
 1. A surface defect inspection apparatus comprising:an illumination optical system that linearly irradiates a beam on asurface of an inspection sample to form a linear illumination region onthe inspection sample surface, wherein the linear illumination opticalsystem is configured to irradiate the beam at a same region of theinspection sample surface a plural number of times, a stage that holdsan inspection sample and configured to be moved in a longitudinaldirection of the linear illumination region at a feed pitch shorter thana longitudinal length of the linear illumination region, the feed pitchbeing variable; and at least one detection optical system that detectsscattered lights scattered the plural number of times from the linearillumination region on the inspection sample surface, wherein the atleast one detection optical system includes a focusing system and amulti-pixel sensor array, and is located perpendicular to a longitudinaldirection of the linear illumination region.
 2. A surface defectinspection apparatus according to claim 1, wherein the multi-pixelsensor array comprises a photodiode array.
 3. A surface defectinspection apparatus according to claim 1, wherein the focusing systemof the at least one detection optical system is configured to focus theplurality of scattered lights to the multi-pixel sensor array, and themulti-pixel sensor array is configured to detect the scattered lights.4. A surface defect inspection apparatus according to claim 1, whereinthe illumination optical system is configured to irradiate beams ontothe surface of the inspection sample from plural directions.
 5. Asurface defect inspection apparatus according to claim 1, wherein theapparatus includes a plurality of detection optical systems.
 6. Asurface defect inspection apparatus according to claim 1, wherein aprocessing unit is configured to process the electrical signal and toclassify kinds of defects based on processing by the processing unit. 7.A surface defect inspection apparatus according to claim 1, furthercomprising means for converting a plurality of scattered lights detectedby the at least one detection optical system into a plurality ofelectric signals, wherein the plurality of electric signals areconfigured to be used to classify defects.
 8. A surface defectinspection method comprising: a step of linearly irradiating a beam on asurface of an inspection sample a plural number of times on a sameregion of the surface of the inspection sample to form a linearillumination region on the inspection sample surface, a step of holdingthe inspection sample by a stage and moving the inspection sample in alongitudinal direction of the linear illumination region at a feed pitchshorter than a longitudinal length of the linear illumination region,the feed pitch being variable, and a step of detecting scattered lightsscattered the plural number of times from the linear illumination regionon the inspection sample surface by at least one detection opticalsystem, wherein the at least one detection optical system includes afocusing system and a multi-pixel sensor array, and is locatedperpendicular to the longitudinal direction of the linear illuminationregion.
 9. A surface defect inspection method according to claim 8,wherein the multi-pixel sensor array is comprised of a photodiode array.10. A surface defect inspection method according to claim 8, furthercomprising focusing, via the focusing system of the at least onedetection optical system, the plurality of scattered lights to themulti-pixel sensor array, and detecting the scattered lights with themulti-pixel sensor array.
 11. A surface defect inspection methodaccording to claim 8, further comprising irradiating, via theillumination optical system, beams onto the surfaces of the inspectionsample from plural directions.
 12. A surface defect inspection methodaccording to claim 8, wherein a plurality of detection optical systemsare provided.
 13. A surface defect inspection method according to claim8, further comprising processing, via a processing unit, the electricalsignal and classifying kinds of defects based on processing by theprocessing unit.
 14. A surface defect inspection method according toclaim 8, further comprising converting a plurality of scattered lightsdetected by the at least one detection optical system to a plurality ofelectric signals, and classifying defects based on the plurality ofelectric signals.